Procalcitonin (PCT) is a precursor substance of serum calcitonin (CT), consisting of 116 amino acids and is a glycoprotein with a molecular weight of approximately 14.5 kDa. Its structure is mainly divided into three parts: the amino-terminal, the procalcitonin segment, and the carboxy-terminal peptide. Under normal physiological conditions, PCT is secreted by thyroid C cells, and its concentration in the blood of healthy individuals is very low, typically less than 0.05 ng/mL. During inflammatory stimuli such as bacterial, fungal, or parasitic infections, especially in sepsis, various tissues and cell types in the body can produce and release PCT into the bloodstream.

Brain natriuretic peptide (BNP) is currently the most widely used biomarker in the diagnosis and treatment of heart failure. It aids in the diagnosis and differential diagnosis of acute and chronic heart failure, risk stratification, monitoring of treatment efficacy, and prognosis assessment. BNP is primarily synthesized and secreted by ventricular muscle cells and increases when the ventricles are overloaded or dilated, making it a useful marker for reflecting changes in ventricular function. It is a specific and sensitive indicator of ventricular dysfunction. The gene encoding human BNP, NPPB, is located on chromosome 1 at 1p36.2. When myocardial cells receive stretch stimuli, they first secrete pre-proBNP...

C-reactive protein (CRP) is an acute-phase protein with a pentameric structure, known for its stability and precision. It is a non-specific marker for inflammation and tissue damage. Under normal conditions, CRP levels in the plasma are very low. However, during acute bacterial infections, malignancies, localized ischemia, or tissue damage, hepatocytes produce large amounts of CRP, causing a sharp increase in its levels within hours. As a result, CRP is a sensitive indicator of the body's inflammatory state and is also used clinically to differentiate between bacterial and viral infections.

The latest management consensus released in 2020 by the European Society of Cardiology (ESC) and the Acute Cardiovascular Care Association (ACCA) specifies that acute chest pain is defined as non-traumatic pain or other discomfort in the chest occurring within 24 hours of onset. According to the location of the chest pain, the front is between the nasal base and the umbilicus, while the back is between the occipital bone and the 12th thoracic vertebra. The nature of the pain includes stabbing, burning, pressure, tightness, heartburn, and similar discomforts.

D-dimer is a degradation product of cross-linked fibrin and serves as an important marker for the activation of the coagulation and fibrinolysis systems in the body. It is widely used in the diagnosis and management of coagulation disorders. In recent years, as research on D-dimer has deepened and detection technologies have advanced, issues related to laboratory testing and clinical application of D-dimer have become increasingly prominent, affecting both laboratory diagnostics and clinical management.